In a conventional ball bearing, as a cage which retains a plurality of rolling elements arranged in a rolling manner between a race surface of an outer ring and a race surface of an inner ring along a circumferential direction, a cage made of steel by means of press forming is generally used. However, in the cage made of steel, when a rotation speed of the bearing becomes fast, friction caused by sliding contact between the rolling element and the cage becomes large and rising temperature of the bearing becomes large, and as a result, seizure of the bearing might be caused. Thus, it is considered to be effective to use the cage formed by injection molding of synthetic resin which is superior to steel in a view of self-lubricant performance, low friction performance, light weight or the like. Generally, polyamide 6 resin, polyamide 66 resin, polyamide 46 resin or the like, which is reinforced by adding glass fiber as needed, is used (see Patent Document 1). Further, in order to further improve dimensional stability, heat resistance and chemical resistance, a cage in which polyamide 9T resin is used is proposed (see Patent Documents 2, 3).